The present invention relates to a dressing wheel. More particularly this invention concerns a method of making such a wheel.
A standard dressing wheel, as for instance used to true a grinding wheel when it has become crowned with use, is comprised of a disk-shaped core or base body centered on an axis and having a surface at which opens an annular groove in which abrasive elements or grinding particles are fixed. These elements are typically real or synthetic mono or polycrystalline diamonds.
Such a dressing wheel is made by enclosing the base body in a negative mold formed of graphite. The abrasive particles are adhered by adhesive and/or galvanically to an inner surface of the mold at a spacing from the periphery of the base body. The annular space between the abrasive particles and the body is packed with a matrix or binding powder and the interstices or pores in the powder are infiltrated by capillary action with a molten solder, drawn into place under a vacuum or atmosphere of protective gas, to bind the powder together and to both the abrasive elements and the base body. Thus the groove is filled with a mass comprised of the abrasive elements, the matrix powder, and the now hard solder. The workpiece is then cooled and stripped out of the mold.
Such a manufacturing process is quite complex, mainly because it requires the use of the negative graphite mold which often cannot be reused. In addition the abrasive elements of this dressing wheel are not very solidly mounted to the base body, mainly because they are separated from them by a considerable mass of the solder-infiltrated matrix powder.
It is therefore an object of the present invention to provide an improved dressing wheel.
Another object is the provision of an improved method of making a dressing wheel which overcomes the above-given disadvantages, that is which is relatively simple so that the wheel can be made inexpensively.
A further object is to provide a particularly robust and durable dressing wheel.
These objects are attained in a dressing wheel having according to the invention a disk-shaped base body centered on an axis and formed with an annular groove also centered on the axis and having an inner surface. A multiplicity of abrasive elements distributed along the groove are in direct contact with the groove inner surface. Matrix powder fills the groove between the elements and between the elements and the groove surfaces. A hardened liquid infiltrating agent fills interstices of the matrix powder.
Such a dressing wheel is made by first positioning abrasive elements along an annular groove opening at a face of a base body and securing the abrasive elements in the groove. Then the groove is filled between the abrasive elements and between the abrasive elements and surfaces of the groove with a fluent matrix powder. Interstices of the matrix powder are then infiltrated with a hardenable liquid infiltrating agent that is hardened to bond the matrix powder to the abrasive elements and to the groove surfaces. An outer surface of the bonded together matrix powder, hardened infiltrating agent, and abrasive elements is then machined off.
This wheel and manufacturing method have several advantages. First of all, there is no need for a sacrificial graphite mold. This alone greatly reduces the costs of manufacturing the wheel. Furthermore the abrasive elements, normally particles of real or synthetic diamond, are in direct contact with the base body, typically formed of steel, so that they are very solidly mounted and can be counted on not to shift even when subjected to exceptional stresses. The amount of matrix powder needed is substantially less than that used in a prior-art dressing wheel, where it must fill the considerable gap between the abrasive elements secured to the inside surface of the negative graphite mold and the groove surfaces, so that on the one hand this expensive material is used sparingly and on the other hand the matrix formed by the matrix powder and the hardened infiltrating agent is of minimal mass and thickness, making the finished wheel much stronger and more effectively anchoring the abrasive elements on the base disk.
According to the invention the outer surface is machined off to impart a predetermined body-of-revolution shape to the disk at the groove. This can be done when the groove opens axially and radially at a corner of the base disk by milling off an axially directed end face of the wheel and forming a frustoconical surface that meets the milled-off end face at a corner where the abrasive elements bedded in their matrix are exposed.
The matrix powder in accordance with the invention includes particles of a liquefiable and hardenable infiltrating agent, e.g. small granules of solder. The solder itself is an unactivated copper-base solder which is a relatively inexpensive product. In this case it is not necessary to operate under a high vacuum or with an expensive inert gas.
To further increase the grinding effectiveness of the finished dressing wheel, the matrix powder and/or the infiltrating agent include particles of carbide, nitride, oxide, or ceramic. This increases the wear resistance of the matrix exposed between the abrasive elements.
In order to increase the bond of the diamond abrasive elements, carbide-formers such as tungsten are added to the matrix powder and/or hardenable infiltrating agent. This simultaneously increases the wear resistance of the matrix and the strength of the bond with the abrasive elements.
The abrasive elements in accordance with the invention are secured in the groove with an adhesive, preferably one with a long setup time. A two-component adhesive can be used, even one that will not stand up to the high temperatures of the infiltrating step, since by the time the workpiece is heated to infiltrate the matrix powder with the liquid infiltrating agent, the matrix powder has already been packed in place and will hold the abrasive elements well enough until the parts cool and the actual bonds are formed. If the abrasive elements are also secured galvanically in the metallic base disk, an electrically conductive adhesive is used so that there is good current flow even in locations where the abrasive particles do not directly contact the base body.
The base body according to the invention is centered on an axis and at least some of the abrasive elements are secured in the groove in a position extending generally perpendicular to, parallel to, or at acute angles to the axis. Thus it is possible to position the abrasive elements for maximum effectiveness in the finished dressing wheel, even stochastically if necessary.